全文获取类型
收费全文 | 140篇 |
免费 | 0篇 |
国内免费 | 2篇 |
专业分类
化学 | 86篇 |
晶体学 | 1篇 |
力学 | 3篇 |
数学 | 16篇 |
物理学 | 36篇 |
出版年
2020年 | 2篇 |
2015年 | 1篇 |
2014年 | 1篇 |
2013年 | 6篇 |
2012年 | 6篇 |
2011年 | 3篇 |
2010年 | 3篇 |
2009年 | 7篇 |
2008年 | 10篇 |
2007年 | 13篇 |
2006年 | 3篇 |
2005年 | 6篇 |
2004年 | 3篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1961年 | 2篇 |
1938年 | 2篇 |
1936年 | 1篇 |
1934年 | 1篇 |
1932年 | 2篇 |
1931年 | 1篇 |
1929年 | 1篇 |
排序方式: 共有142条查询结果,搜索用时 15 毫秒
1.
G. N. Merrill 《Journal of Physical Organic Chemistry》2007,20(1):19-29
Ab initio molecular orbital calculations were carried out on epibromohydrin (EBH) and epichlorohydrin (ECH) in an attempt to elucidate their reactivity with respect to a hard nucleophile, hydroxide. These systems were modeled in both the gas phase and a polar solvent under basic conditions. In the gas phase, it was determined that a direct displacement mechanism (nucleophilic attack at the C1 position) was operative for EBH, while an indirect pathway (nucleophilic attack at the C3 position and subsequent intramolecular displacement) was followed for ECH. In an acetone solution, only the indirect displacement mechanism was found to occur. An electrostatic argument is advanced to account for this behavior in polar solution. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
2.
Zhu H Chai J Chandrasekhar V Roesky HW Magull J Vidovic D Schmidt HG Noltemeyer M Power PP Merrill WA 《Journal of the American Chemical Society》2004,126(31):9472-9473
The reaction of beta-diketiminated aluminum(I) monomer LAl with a large bulky azide N3Ar' (L = HC(CMeNAr)2, Ar' = 2,6-Ar2C6H3, Ar = 2,6-iPr2C6H3) in the temperature range from -78 degrees C to room temperature affords two different isomers 2 and 3, which have been characterized by spectroscopic and X-ray structural analyses, as well as elemental analysis. The variable-temperature 1H NMR kinetic studies of this reaction indicate the existence of the monomer LAlNAr' (1) at low temperature and the thermal stability of the compounds increases in the order of 1 < 2 < 3. 相似文献
3.
A. R. Hutter R. J. Larsen H. Maring J. T. Merrill 《Journal of Radioanalytical and Nuclear Chemistry》1995,193(2):309-318
Continuous measurements of atmospheric222Rn were made for the past three years by the Environmental Measurements Laboratory (EML) at the Atmosphere/Ocean Chemistry Experiment site located at Tudor Hill, Bermuda and at the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory Mauna Loa Observatory. The222Rn analyzer is based on the two-filter tube method. At the Bermuda site, monthly median222Rn concentration range from 50 to 700 mBq m–3, and the concentrations vary seasonally, with a maximum in the winter and a minimum in the summer. The concentrations are significantly elevated when local winds traverse the island. At MLO, monthly median222Rn concentrations range from 100 mBq m–3 during the fall months to 400 mBq m–3 during the spring months. The springtime maximum values correspond to periods of rapid transport in the free troposphere from the Asian continent, corroborated by backward air mass trajectories. The222Rn data are also used to help decipher local daily upslope/downslope conditions present at MLO. This study illustrates the value of atmospheric222Rn monitoring, when screened through the filter of local meteorology, in studying the transport of continental air to the oceans, as well as the dynamics of local meteorological effects. 相似文献
4.
The present work discusses the grafting by electron beam irradiation of poly(ethylene oxide) (PEO) star-shaped polymers onto porous expanded polytetrafluoroethylene (EXPTFE) surfaces. The resulting materials are intended to combine the good biocompatible properties of PEO with the outstanding mechanical properties of PTFE. The star-shaped PEOs were synthesized via anionic polymerization. 3 Mev electron beam irradiation was applied to graft these PEO stars onto porous EXPTFE surfaces. The hydrophobic EXPTFE surface had to be pre-modified with N-vinylpyrrolidone. ESCA was used to quantify the amount of grafted star-shaped PEO. Unmodified EXPTFE surfaces are well known, when implanted in a body, to be rapidly covered by a layer of cells and fibrin. The EXPTFE coated with PEO were implanted in the peritoneal cavity of rats (or under the back skin). This implantation did not induce any inflammation reactions and SEM analysis had attested the absence of adsorbed cells and fibrin. The glucose diffusion properties of these membranes were studied by a lag time analysis method and compared to those of pure PEO hydrogels. As expected, glucose diffuses through the hydrogel coated membrane and diffusion is not affected by the presence of the EXPTFE membrane. 相似文献
5.
Treatment of thieno[2,3-b]pyridine (1a) with n-butyllithium in hexane-tetramethylethylene-diamine at ?70° plus subsequent addition of dimethylformamide produced 2-formyl-Ia (66%). Halogen-metal exchange between 3-bromothieno[2,3-b]pyridine and n-butyllithium was effected in ether at ?70. Further reaction of the 3-lithio-Ia intermediate with a variety of carbonyl compounds gave 3-substituted thieno[2,3-b]pyridines bearing formyl (77%), acetyl, benzoyl, chloroacetyl, ethoxycarbonyl, N-phenylcarbamyl, and diphenyl hydroxymethyl groups. Common characteristics of these derivatives in pmr and mass spectra are noted. 相似文献
6.
B. Mears P. R. Pine H. W. Doughty B. Freeman J. Guzmán A. Rancano T. L. Kelley J. J. Melloy H. A. Fales T. Callan R. T. P. Jones B. Tougarinov H. Hölemann C. Frick H. Engemann A. Schleicher W. T. Schrenk Ph. H. Delano J. L. Merrill A. S. Russell S. W. Rowell K. S. Jackson N. H. Furman M. I. Schubin K Anderson H. Swett Ella M. Collin H. J. S. Sand L. F. Yntema und D. D. Peirce 《Fresenius' Journal of Analytical Chemistry》1932,87(5-6):214-224
Ohne Zusammenfassung 相似文献
7.
E. Müller A. Luber C. Riess A. Papayannis E. Weinberger K. Ziegler V. Kubelka V. Nêmec F. Berka F. A. Ssapegin M. S. Strojew I. D. Clarke R. W. Frey M. Bergmann F. Mecke G. F. Smith V. R. Sullivan L. J. Weiland W. J. Seymour A. W. Greenstein E. Stiasny H. B. Merrill C. Benrud J. A. Wilson 《Analytical and bioanalytical chemistry》1938,114(7-8):310-319
8.
9.
Some metal ion complexing properties of the ligand PDAM (1,10-phenanthroline-2,9-dicarboxamide) in aqueous solution are reported. Using UV-visible spectroscopy to follow the intense π-π* transitions of PDAM as a function of metal ion concentration, log K(1) values in 0.1 M NaClO(4) and at 25 °C are, for Cu(II), 3.56(5); Ni(II), 3.06(5); Zn(II), 3.77(5); Co(II), 3.8(1); Mg(II), 0.1(1); Ca(II), 1.94(4); and Ba(II), 0.7(1). For more strongly bound metal ions, competition reactions between PDAM and EDTA (ethylenedinitrilo-tetraacetic acid) or tetren (1,4,7,10,13-pentaazatridecane), monitored following the UV spectrum of PDAM, gave the following log K(1) values in 0.1 M NaClO(4) and at 25 °C: Cd(II), 7.1(1); Pb(II), 5.82(5); In(III), 9.4(1); and Bi(III), 9.4(1). The very low log K(1)(PDAM) values for small metal ions such as Cu(II) or Zn(II) are unprecedented for a phen-based ligand (phen = 1,10-phenanthroline), which is rationalized in terms of the low basicity of the N donors of the ligand (pK(a) = 0.6) and the fact that PDAM has a best-fit size corresponding to large metal ions of ionic radius ~1.0 ?. Large metal ions with ionic radius ≥1.0 ? show large increases in log K(1) relative to their phen complexes, which in turn produces unparalleled selectivities, such as a 3.5 log units greater log K(1)(PDAM) for Cd(II) than for Cu(II). PDAM shows strong fluorescence in aqueous solution, suggesting that its carboxamide groups do not produce a fluorescence-quenching photon-induced electron transfer (PET) effect. Only Ca(II) produces a weak CHEF (chelation enhanced fluorescence) effect with PDAM, while all other metal ions tested produce a decrease in fluorescence, a CHEQ (chelation enhanced quenching effect). The production of the CHEQ effect is rationalized in terms of the idea that coordination of metal ions to PDAM stabilizes a canonical form of the carboxamide groups that promotes a PET effect. 相似文献
10.
Richard V. Whiteley Jr. Raymond M. Merrill 《Fresenius' Journal of Analytical Chemistry》1982,311(1):7-10
Summary A method for the determination of quantities of 0.5–500 g of Cr(III) in the presence of chromates and dichromates is described. The samples are dissolved in an aqueous solution buffered at pH 7.0; the Cr(III) is selectively chelated with 2-thenoyltrifluoroacetone and extracted into xylene. The extracted chromium is analyzed using inductively coupled plasma emission spectrometry. Extraction of 1.0 g Cr(III) from 5.0 mg K2Cr2O7 was accomplished and easily determined in a volume of 25 ml of xylene. The relative standard deviation for the determination of Cr(III) contents ranging from 4.0 × 10–8 g/ml to 2.0 × 10–8 g/ml was ± 0.079. Using a minimum signal to noise ratio of 101, the detection limits of the method were determined to be approximately 2.0 × 10–8 g/ml xylene. Chloride, high surface area silica, and easily oxidized amorphous boron give rise to only minor interferences.
This work was supported by the U.S. Department of Energy (DOE) under contract number DE-AC04-76-DP00789
A U.S. DOE facility 相似文献
Analyse von Cr(III)-Spuren in Chromaten durch Extraktion und ICP-Atomemissionsspektrometrie
Zusammenfassung Ein Verfahren wird beschrieben zur Bestimmung von 0,5–500 g Cr(III) in Gegenwart von Chromaten und Dichromaten. Die Proben werden in Pufferlösung pH 7,0 gelöst, und 2-Thenoyltrifluoraceton behandelt und Cr(III) selektiv mit Xylol extrahiert. Die Bestimmung erfolgt durch ICP-Spektrometrie. 1,0 g Cr(III) konnte von 5,0 mg K2Cr2O7 getrennt und in einen Volumen von 25 ml Xylol bestimmt werden. Die relative Standardabweichung im Bereich von 4,0 · 10–8 bis 2,0 · 10–7 g Cr(III)/ml betrug ± 0,079. Bei einem Verhältnis SignalUntergrund = 101 wurden Nachweisgrenzen um 2,0 · 10–8 g/ml gefunden. Störungen durch Chlorid, Siliciumdioxid und amorphes Bor sind gering.
This work was supported by the U.S. Department of Energy (DOE) under contract number DE-AC04-76-DP00789
A U.S. DOE facility 相似文献